Project Summary The goal of this project is to understand the role of WIP1 (Wild-type p53 Induced Phosphatase 1) mutations in clonal hematopoiesis. Hematopoiesis is a hierarchically organized process of blood cell production, with hematopoietic stem cells (HSCs) at the top of the hierarchy. HSCs reside in the bone marrow and are characterized by the ability to self-renew or differentiate into various types of mature blood cells. HSCs can acquire somatic mutations with age, and clones harboring certain mutations can gain a competitive advantage that manifests as expansion of the clone. This phenomenon is termed clonal hematopoiesis, and is associated with increased risk of hematologic diseases and all-cause mortality. WIP1 is one of the most frequently mutated genes in clonal hematopoiesis, but very little is understood about the effect of WIP1 mutations on HSC function. The presence of expanded WIP1-mutated hematopoietic clones with age indicates that mutant WIP1 affects the regulation of hematopoiesis. Furthermore, WIP1 mutations were found to be enriched in the blood of therapy-related myelodysplastic syndrome (t-MDS) patients compared to de novo MDS patients, suggesting that the selective pressure of stress may further contribute to the expansion of WIP1-mutated clones. Our overarching goal is to gain insight into the mechanisms through which WIP1 mutations drive hematopoietic clonal expansion with age and stress. We hypothesize that HSC clones with truncated WIP1 have a competitive advantage over their wild-type counterparts, due to the role of WIP1 in regulating cell response to cell cycle checkpoints and apoptosis. To test this hypothesis, we will re-create the WIP1 mutation in hematopoietic cells and determine the biochemical and cellular phenotypes of the mutant. We will also examine the effect of the WIP1 truncating mutation on HSC function in vivo. We will then determine the mechanism of WIP1 clonal expansion following cellular stress. Together, these proposed studies will lend insight into the role of WIP1 in HSC biology, and will help us achieve the long-term goal of facilitating healthy aging of stem cells.